Method of preparing trifluoromethyliminosulfur difluorides



United States Patent METHOD OF PREPARING TRIFLUOROMETI-IYL- MINOSULFURDIFLUGRIDES Charles W. Tullock, Wilmington, DeL, assignor to E. I. duPont de Nemours and Company, Wilmington, Del., a corporation of DelawareN0 Drawing. Application April 28, 1958 Serial No. 731,113

9 Claims. (Cl. 260-543) This invention relates to a process forpreparing iminosulfur dihalides. More particularly; it relates to aprocess for preparing trifluoromethyliminosulfur difluoride.

Organic iminosulfur difluorides represent a new classoffluorine-containing compounds which are described in apending andcoassigned application, Serial No. 612,876, filed September 28, 1956, byWilliam Channing Smith. These compounds are characterized by having thefluorine atoms attached to a tetravalent sulfur atom which in turn isbonded by a double bond to an imino nitrogen atom of an organiccompound. An important member of this group of' compounds istrifluoromethyliminosulfur difluoride whose structural formula is CF--N=SF Trifluoromethyliminosulfur difluoride is a gas at normalatmospheric temperature and pressure. It can be condensed in trapscooled with carbon dioxide-acetone solutions or liquid nitrogen to aliquid which boils at about -5 to 6 C. The compound is a highly reactivematerial and is preferably stored under anhydrous conditions incontainers which are resistant to chemical attack. Because of itsreactivity, it is valuable as an intermediate in the preparation ofother fluorine-bearing compounds. It reacts with alcohols, phenols,hydrocarbons and thelike to form compounds which contain thetrifluoromethyliminosulfur group. Trifluoromethyliminosulfur difluoridecan be employed as a polymerization catalyst for fluoroolefins and as asource of tetrafluoroethylene, a technically important fluoroolefln. Anobject of this invention is, consequently, provision of a novel methodfor the manufacture of trifluoromethyliminosulfur difluoride.

In accordance with the above-mentioned and other objects, there is nowprovided a process for preparing trifluoromethyliminosulfur difluoridein good yield from available low cost materials. The process consists inreacting an inorganic thiocyanate and chlorine with a fluoride of ametal of atomic number 11 through 82 of groups I-A, LB, II-B and IV-A ofthe periodic table as set forth in Demings General Chemistry (John Wiley& Sons, Inc;, 5th ed), 1944. I

The term metals, as employed in this invention with respect to thefluorides, means the elements which are classified as metals in chapter11 of Demings textbook and in the periodic table, referred to above. Theelements of groups I-A, LB, 11-13 and IV-A of atomic number 11 through82 which are classified as metals are sodium, potassium, rubidium,caesium, copper, silver, gold, zinc, cadmium, mercury, germanium, tinand lead. Examples of fluorides of metals which are operable in theprocess of this invention are sodium fluoride (NaF), potassium fluoride(KF), caesium fluoride (CsF), copper fluoride (CuF silver fluoride(AgF), Zinc fluoride (ZnF mercury fluorides (Hg F and HgF tin fluorides(SnF and SnF and lead fluoride (PbF The fluorides which are preferredbecause of cost and availability for use in the process are thefluorides of the metals of groups I-A and II-B with atomic numbers of 11Patented Apr. 21, 1959 through 80. Especially preferred are thefluorides of sodium and potassium.

Any inorganic thiocyanate stable at ordinary temperatures and pressuresis operable in the process of the invention. The character of theinorganic group which is bonded to the thiocyanate radical is notcritical for operability in the process since this group does not form apart of the desired end product, that is trifiuoromethyliminosulfurdifluoride. The preferred inorganic thiocyanates are those which arereadily available at low cost, for example, ammonium thiocyanate and thethiocyanates of the alkali and alkaline earth metals. The thiocyanatesof lithium, sodium, potassium, magnesium, calcium and barium, as Well asammonium, are illustrative of the thiocyanates which are well suited foruse in the process. If desired, the thiocyanate can be preformed in thereaction vessel and then reacted with chlorine and a metal fluoride.Both the thiocyanate and fluoride reactants are preferably used incomminuted form to obtain the maximum rate of reaction and reduce thetime required to complete the reaction.

The third component employed in the process, that is, chlorine, is areadily available commercial product.

The reactants need not be especially purified for use in the process butthey should be reasonably free of moisture sincetrifluoromethyliminosulfur difluoride reacts with water. For maximumyield of product, it is preferable, therefore, to dry the reactantsprior to use. This step in the process is not essential for operabilityand is used solely as a means of obtaining the highest yield of product.Mixed metal fluorides and mixed inorganic thiocyanates can be employedwithout adversely affecting operability. Commercial grade chemicals canbe employed satisfactorily.

The reaction of the inorganic thiocyanate, metal fluoride and chlorineis conducted under substantially anhydrous conditions in either a batchor continuous flow process. In either process the reaction chamber ispreferably made of material resistant to chemical attack by hydrogenfluoride, for example, stainless steel.

In a batch process a vessel capable of withstanding pressure ispreferably flushed with an inert gas, for example, nitrogen, to displacethe air and is then charged with the inorganic thiocyanate and the metalfluoride. The chamber is evacuated to a low pressure, for example, 10mm. or less, and then charged with chlorine. The reaction chamber isclosed and the mixture then heated at the desired temperature withsuitable mechanical agitation.

The mechanism of the reaction is not clearly understood but it isobvious that the sulfur and fluorine in the final product are obtainedfrom the inorganic thiocyanate and fluoride, respectively. The chlorinereactant is converted to a by-product inorganic chloride.

It is not essential for operability that the reactants be used in anyparticular ratios. However, in order to obtain maximum yield oftrifluoromethyliminosulfur difluoride certain ratios of reactants arepreferred. Generally the molar ratio of thiocyanate groups (SCN) t0fluoride groups (P) in the reactants is not less than about 1:1 or morethan about 1:20; preferably the ratio for these groups lies between 1:3and 1:10. Suflicient chlorine is preferably used to react withsubstantially all of the inorganic cations present. Lower quantities ofchlorine can, however, be employed without affecting operability sinceunreacted components can be recovered and reused.

The temperature of the reaction is kept as low as operability permits.It will generally lie between about 50 and 500 C. The preferredtemperature range for optimum yield lies between about and 400 C.

Excessively high temperatures are not necessary and provide little or noadvantage in economy of operation or yield of desired product.

Heating of the reactants can be accomplished by a stepwise procedurewherein the reactants are maintained for short periods of time atprogressively higher temperatures. This procedure permits smoothoperation of the process and avoids sudden increases in pressure in thereaction vessel. However, this procedure is not essential foroperability. The reactants can, if desired, be heated in one step to thereaction temperature. The time of heating is generally between about 2hours to about'48 hours.

The pressure employed in a batch process is generally autogenous and canbe between about 5 atmospheres and 50 atmospheres. During the reactionperiod, the contents of the vessel are preferably mixed, for example, bymechanical stirring or shaking.

The process of the invention can also be conducted by a continuous flowmethod wherein, for example, a mixture of thiocyanate and fluoride isplaced in a tube of corrosion resistant material and chlorine gas passedover the mixture as it is heated to the desired reaction temperature.The volatile trifluoromethyliminosulfur difluoride can be collected intraps cooled with, for example, solid carbon dioxide-acetone solution orliquid nitrogen. A continuous process is usually Operated at atmosphericpressure although it can be operated at pressures that are higher orlower than atmospheric.

Trifluoromethyliminosulfur difluoride can be collected, as describedpreviously, in corrosion-resistant traps or pressure vessels which arecooled by any suitable means to a temperature of about 20 C. or lower.The crude product can be purified by distillation through a conventionallow temperature fractionation unit. The pure product boils atapproximately --5 to 6 C. but fractions boiling between about 3' to -8C. are substantially pure.

The following examples, in which quantities are expressed as parts byweight, illustrate the process of this invention. In each of theexamples, a vessel is used which is lined with Hastelloy C and iscapable of withstanding pressure. Hastelloy C is a well knownchemicallyresistant alloy of nickel, iron and molybdenum.

Example I A. A pressure vessel (capacity, 1000 parts of water) ischarged with 41 parts of sodium thiocyanate and 135 parts of sodiumfluoride. The pressure vessel is then flushed with nitrogen, closed andevacuated to about 1 mm. pressure. It is then charged with 106 parts ofchlorine gas. The vessel is heated with agitation at 75 C. for 3 hours,150 C. for 1 hour and 235 C. for 4 hours. The pressure vessel is cooledand the volatile products are vented into a stainless steel cylinder.There is obtained 47 parts of volatile products which are distilledthrough a low temperature fractionation unit to yield 17 parts (about22% yield) of trifluoromethyliminosulfur diffuoride of approximately 95%purity, as determin by infrared analysis.

B. A mixture of 62 parts of sodium thiocyanate, 175 parts of sodiumfluoride and 142 parts of chlorine is heated as described in part A ofthis Example at 75 C. for 3 hours, 150 C. for 1 hour and 235 C. for 6hours. There is obtained 92 parts of volatile products which aredistilled through a low temperature fractionation unit to yield 57 parts(about 49% yield) of trifluoromethyliminosulfur difluoride, boiling at 3to 5 C.

Example 11 A pressure vessel (capacity, 500 parts of water) is chargedwith 32 parts of potassium thiocyanate, 90 parts of sodium fluoride and70 parts of chlorine as described in Example I. The reactants are heatedwith agitation at 150 C. for 1 hour and 235 C. for 4 hours. There isobtained 36 parts of volatile products which are shown by infraredanalysis to contain, on a molar basis, 60% of trifluoromethyliminosulfurdifluoride. The yield of desired product, based on potassiumthiocyanate, is approximately 50%.

Example III A pressure vessel (capacity, 500 parts of water) is chargedwith 25 parts of calcium thiocyanate, parts of sodium fluoride and 68parts of chlorine as described in Example I. The reactants are heatedwith agitation at 75 C. for 1 hour, C. for 1 hour, and 235 C. for 6hours. There is obtained 13 parts of volatile products which are shownby infrared analysis to contain a substantial quantity (more than 50%)of trifluoromethyliminosulfur difluoride.

Examples I through HI illustrate the process of the invention using thethiocyanates of the alkali and alkaline earth metals, that is, themetals of groups I-A and II-A of the periodic table. However, inorganicthiocyanates broadly can be employed in the process as illustrated inExamples IV and V which follow.

Example IV A pressure vessel (capacity, 200 parts of water) is chargedwith 7 parts of ammonium thiocyanate, 60 parts of sodium fluoride and 29parts of chlorine as described in Example I. The reactants are heatedwith agitation at 75 C. for 1 hour, 150 C. for 1 hour, and 235 C. for 6hours. There is obtained 20 parts of volatile products which are shownby infrared analysis to contain, on a molar basis, 35% oftrifluoromethyliminosulfur difluoride. The yield of desired product,based on ammonium thiocyanate, is about 60%.

Example V A mixture of 50 parts of lead thiocyanate, 90 parts of sodiumfluoride and 66 parts of chlorine is heated as described in Example IV.There is obtained 32 parts of volatile products which are shown byinfrared analysis to contain at least 50% of trifluoromethyliminosulfurdifluoride.

Examples of other thiocyanates which can be employed in the process arebarium thiocyanate, silicon tetrathiocyanate, copper thiocyanate, silverthiocyanate, ferric and ferrous thiocyanates, nickel thiocyanate,manganese thiocyanate, mercuric thiocyanate, mercurous thiocyanate, andzinc thiocyanate. Ammonium thiocyanate and the thiocyanates of thealkali metals and alkaline earth metals are preferred because ofavailability and cost.

Example VI A mixture of 16 parts of potassium thiocyanate, 60 parts ofpotassium fluoride and 35 parts of chlorine is heated as described inExample I at 75 C. for 1 hour, 150 C. for 1 hour, and 235 C. for 6hours. There is obtained 16 parts of volatile products which are shownby infrared analysis to contain, on a molar basis, 5-10% oftrifluoromethyliminosulfur difluoride. The low yield of desired productis attributed to the relatively large particle size of the potassiumfluoride and to traces of water which it retains. Potassium fluoride isa very hygroscopic material. More thorough drying of this reactantresults in higher yields of trifluoromethyliminosulfur difluoride.

Examples I through VI illustrate the use in the process of fluorides ofgroup I metals of atomic number 11 or higher. Other metal fluorides ofthis group which can be employed are caesium fluoride, copper fluorideand silver fluoride.

Example VII A mixture of 32.4 parts of sodium thiocyanate, 150 parts ofzinc fluoride and 86 parts of chlorine is heated with agitation asdescribed in Example I at 75 C. for 1 hour, 150 C. for 1 hour, and 235C. for 6 hours. There is obtained 37 parts of volatile products whichare shown by infrared analysis to contain a substantial quannasauaa tity(more than 50%) of trifluoromethyliminosulfur difluoride.

Example VII illustrates the process of the invention employing thefluoride of a group II-B metal. Fluorides of metals of group IV-A can beemployed in the process as described in the examples. Thus, tintetrafluoride and lead fluoride can be used in place of the zincfluoride of Example VII. For example, trifluoromethyliminosulfurdifluoride is obtained by heating mixtures of (a) stannic fluoride,ammonium thiocyanate and chlorine, and (b) lead fluoride, leadthiocyanate and chlorine.

Since obvious modifiications in the invention will be evident to thoseskilled in the chemical arts, I propose to be bound solely by theappended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. The process for the preparation of trifluoromethyliminosulfurdifluoride which comprises reacting together an inorganic thiocyanate,chlorine and a fluoride of a metal of atomic number 11-82, inclusive,selected from the metals of groups I-A, I-B, -II-B and IV-A of theperiodic table.

2. The invention of claim 1 wherein the inorganic thiocyanate isselected from the class consisting of the alkali and alkaline earthmetal and ammonium thiocyanates.

3. The invention of claim 1 wherein the molar ratio of thiocyanate tofluoride groups in the reactants is between 1:1 and 1:20.

4. The invention of claim 3 wherein said ratio is between ]:3 and 1:10.

5. The invention of claim 1 wherein the metal fluoride is that of ametal of the group consisting of sodium,

potassium and zinc.

6. The process for the preparation of trifluoromethyliminosulfurdifluoride which comprises reacting together sodium thiocyanate,chlorine and a fluoride of a metal of atomic number 1l-82, inclusive,selected from the metals of groups I-A, I-B, II-B and IV-A of theperiodic table.

7. The process for the preparation of trifluorornethyliminosulfurdifluoride which comprises reacting together potassium thiocyanate,chlorine and a fluoride of a metal of atomic number 11-82, inclusive,selected from the metals of group I-A, I-B, II-B and IV-A of theperiodic table.

8. The process for the preparation of trifluoromethyliminosulfurdifluoride which comprises reacting together ammonium thiocyanate,chlorine and a fluoride of a metal of atomic number 11-82, inclusive,selected from the metals of groups I-A, I-B, II-B and IV-A of theperiodic table.

9. The process for the preparation of trifluoromethyliminosulfurdifluoride which comprises reacting together lead thiocyanate, chlorineand a fluoride of a metal of atomic number 11-82, inclusive, selectedfrom the metals of groups I-A, I-B, II-B and IV-A of the periodic table.

No references cited.

1. PROCESS FOR THE PREPARATION OF TRIFLUOROMETHYLIMINOSULFUR DIFLUORIDEWHICH COMPRISES REACTING TOGETHER AN INORGANIC THICOYANATE, CHLORINE ANDA FLUORIDE OF A METAL OF ATOMIC NUMBER 11-82, INCLUSIVE, SELECTED FROMTHE METALS OF GROUPS I -A,I-B, II-B AND IV-A OF THE PERIODIC TABLE.